1. Prior Art Skin Cooling
The principal methods presently used for skin cooling before or during the laser treatment involve the use of a cold contacting window or cryogenic spray device. Cryogenic spray directly to the skin may reduce a skin temperature below 0 C but can freeze the skin and cause significant damage to it. Typical cold contacting windows of the prior art utilize ice water at 0 C can cool the surface of the skin to as low as about 4 C. But prior art ice water cooled cold contact window devices are inadequate to remove enough heat to prevent unwanted surface tissue damage in many applications.
Three prior art techniques are described in the following United States patents: C. Chess, Apparatus for treating cutaneous vascular lesions, U.S. Pat. No. 5,486,172; Anderson et al., U.S. Pat. No. 5,595,568; and C. Chess, Method for treating cutaneous vascular lesions, U.S. Pat. No. 5,282,797. All of these devices and methods provide for the cooling of the skin down to temperatures of about 4 C but not below it.
A different technique is described by J. S. Nelson et al., in the article “Dynamic Epidermal Cooling in Conjunction With Laser-Induced Photothermolysis of Port Wine Stain Blood Vessels, Lasers in Surgery and Medicine 1996;19:224-229. In this technique the direct cryogenic spray to the skin surface is used before the laser pulse delivery. This method is normally not satisfactory. The surface gets too cold and the subsurface layers are not sufficiently cooled so that unwanted damage occurs at the surface because the tissue gets too cold from the cryogen and/or unwanted damage occurs in the immediate subsurface layers because the tissue gets too hot from the laser beam.
2. Selective Photothermolysis
Dr. Leon Goldman and Dr. Rex Anderson developed the technique known as selective photothermolysis. This technique involves the use of a laser beam having absorption in targeted tissue much higher than in other tissue. Blood has very high absorption of laser radiation at about 530 nm and 575-590 nm. These frequencies are available from the double frequency Nd-YAG laser producing 532 nm light and by an argon laser producing 530 nm. Dye lasers at 577, 585 and 587 are also used in techniques that target blood vessels. These techniques have proven very successful in treating conditions known as port wine stains when the blood vessels are small and near the skin surface. The techniques do not work well for deeper, larger blood vessels.
What is needed is a better laser surgery cooling method to better control tissue temperature during laser treatments.